An extension of the Swift String type to provide snake case formatting.

String+SnakeCase.swift

/// An extension to format strings in *snake case*.
extension String {
  
    /// A collection of all the words in the string by separating out any punctuation and spaces.
    var words: [String] {
        return components(separatedBy: CharacterSet.alphanumerics.inverted).filter { !$0.isEmpty }
    }

    /// Returns a lowercased copy of the string with punctuation removed and spaces replaced
    /// by a single underscore, e.g., "the_quick_brown_fox_jumps_over_the_lazy_dog".
    ///
    /// *Lower snake case* (or, illustratively, *snake_case*) is also known as *pothole case*.
    func lowerSnakeCased() -> String {
        return self.words.map({ $0.lowercased() }).joined(separator: "_")
    }

    /// Returns an uppercased copy of the string with punctuation removed and spaces replaced
    /// by a single underscore, e.g., "THE_QUICK_BROWN_FOX_JUMPS_OVER_THE_LAZY_DOG".
    ///
    /// *Upper snake case* (or, illustratively, *SNAKE_CASE*) is also known as
    /// *screaming snake case*.
    func upperSnakeCased() -> String {
        return self.words.map({ $0.uppercased() }).joined(separator: "_")
    }

    /// Returns a copy of the string with punctuation removed and spaces replaced by a single
    /// underscore, e.g., "The_quick_brown_fox_jumps_over_the_lazy_dog". Upper and lower
    /// casing is maintained from the original string.
    func mixedSnakeCased() -> String {
        return self.words.joined(separator: "_")
    }

}